Face detection and tracking is well known in image processing for example as described in European Patent No. EP2052347 (Ref: FN-143). These techniques enable one or more face regions within a scene being imaged to be readily delineated and to allow for subsequent image processing based on this information. Such image processing can include face recognition which attempts to identify individuals being imaged; auto-focussing by bringing a detected and/or selected face region into focus; or defect detection and/or correction of the face region(s).
It is well known that anthropometric information can be employed in processing face regions. For example, knowledge of an expected face size can be used for in face detection or filtering for example, for example, for falsing analysis of red-eye candidates as described in EP1654865 (Ref: FN-101-CIP).
However, problems can occur if a scene being imaged includes any faces which do not conform to common anthropometric rules. For example, if a scene includes a billboard with a very large human face, processing based on common anthropometric rules could indicate a real subject much closer to the camera than the billboard. This could for example, indicate that the camera should focus at a much shorter distance and if it were to do so, an out of focus image would be produced.
Correspondingly, if a scene includes a small child, then detection of their face could indicate a subject much further from the camera than the child. This could for example, indicate that the camera should focus at a much longer distance and again, if it were to do so, an out of focus image would be produced.
For the purposes of the present disclosure, the term “false face” will be used to indicate regions of an image including detected faces which do not conform to normal anthropometric rules.
In some cases, failure to appreciate that a false face has been detected could cause an isolated image to be acquired with incorrect focus, and in a video camera, capturing a stream of images of a scene, it is possible that the camera might lose its ability of focus properly.
Nonetheless, it will be appreciated that the above outlined problems could equally arise if attempting to base image processing on any falsely detected object. For example, some image processing could be based on rules relating to the dimensions of automobiles and clearly image of false automobiles, for example, displayed on billboards, could be captured which could cause problems.